Handshake Solutions
HT80C51 User Manual
Memory Organization – Special Function Registers
Page 14 of 132
© Philips Electronics N.V. 2005
2.5.1.
Accumulator ACC
ACC is the Accumulator register. The mnemonics for Accumulator-Specific instructions, however, refer
to the Accumulator simply as A.
ACC (A)
Accumulator
addr = E0H
reset value = 00H
bits
7
6
5
4
3
2
1
0
ACC
2.5.2.
Register B
The B-register is used during multiply and divide operations. For other instructions it can be treated as
another scratch pad register.
B
Register B
addr = F0H
reset value = 00H
bits
7
6
5
4
3
2
1
0
B
2.5.3.
Program Status Word PSW
The program status word (PSW) register contains program status information as detailed below.
PSW
Program Status Word
addr = D0H
reset value = 00H
bits
7
6
5
4
3
2
1
0
CY
AC
F0
RS1
RS0
OV
-
P
bit
symbol
function
PSW.7
CY
Carry Flag.
PSW.6
AC
Auxiliary Carry Flag.
PSW.5
F0
Flag 0 available to the user for general purpose.
PSW.4
PSW.3
RS1
RS0
0 0
0 1
1 0
1 1
Register Bank selector bit 1.
Register Bank selector bit 0.
(RS1, RS0) select the register bank as follows:
Bank 0
(00H .. 07H)
Bank 1
(08H .. 0FH)
Bank 2
(10H .. 17H)
Bank 3
(18H .. 1FH)
PSW.3
RS0
Register Bank selector bit 0 (see note).
PSW.2
OV
Overflow Flag.
PSW.1
-
Usable as a general-purpose flag.
PSW.0
P
Parity flag. Set/cleared by hardware each instruction cycle to indicate an
odd/even number of ‘1’ bits in the accumulator, that means even parity.
2.5.4.
Stack Pointer SP
The Stack Pointer (SP) register is 8 bits wide. It is incremented before data is stored during PUSH and
CALL executions. While the stack may reside anywhere in on-chip RAM, the Stack Pointer is initialized
to 07H after a reset. This causes the stack to begin at locations 08H.
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